Absolutely it would! I've got an old buddy I met through cosplaying who is a MtF Transgendered person. Because her body is naturally male, she uses the fact that she has a little extra pounds to her advantage. Just recently she rocked a corset and padded her hips and bra just a little for a Lumpy Space Princess costume, and it looked fabulous.

So yes, having a few extra pounds can really give you an advantage when you crossplay. Use it to your advantage if you've got it!